There is a need for inexpensive, compact, high-efficiency oxygen concentrators comprised of compressors and vacuum pumps to drive the pressure-swing and/or vacuum/pressure-swing absorption cycles that separate oxygen from ambient air, such as for therapeutic use in patients with chronic obstructive pulmonary disease (COPD). Such oxygen concentrators typically come in stationary, transportable, and portable varieties. Patients generally prefer more and more the smaller, transportable and portable devices when the patients are still ambulatory. These smaller units have the most severe demands for compactness and weight, plus efficiency (as that drives the duration of the portable battery power source). Vibration can also be a problem when carrying or wearing a portable concentrator.
Stationary concentrators are more cost-driven designs and use a pressure-swing adsorbent (PSA) cycle in which all air pumping in the absorbent beds is done at or above ambient pressure, enabling the use of inexpensive compressors to move the air. In portables however, it is preferred to use vacuum-pressure adsorbent swing (VPSA) cycles, in which the lower-pressure portions of the cycle are sub-atmospheric, because the known absorbents can deliver more oxygen per unit mass of absorber material when the pressures are at such ‘vacuum’ levels. Nonetheless, the need for these pumps (compressors or compressor-vacuum combinations) must also provide breathable quality gas, which can require that they be non-lubricated devices (i.e., do not use oils for lubrication). To date, all such concentrators have been low-stroke reciprocating devices driven with conventional motors.
There is a long-held need for compact, low-vibration, efficient pressure-vacuum combination pumps and compressors that operate without oils and cost no more than conventional reciprocating types.
Existing patents disclose basic kinematics that resemble some elements of the kinematics arrangements described herein. For example, U.S. Pat. No. 2,831,438 to Guinard describes a rotary piston pump having crossed-piston geometry with two sets of cross pistons riding on sliding “sole plates. (a scotch-yoke variant). Moreover, the Guinard system has a crankshaft that is directly connected to a rotor housing. U.S. Pat. No. 2,683,422 to Richards describes a rotary engine or pump having a similar kinematic geometry to the present disclosure, that is epicyclic motion, with a crankshaft rotating at twice the speed of the cylinders to give relative reciprocation between pistons and cylinders, but Richards drives the cylinders, requiring a gear to impart the required motion to the crank (itself a complex hollow construction over a stationary eccentric), and with separately attached cylinders at each piston face, which makes for a cumbersome construction that is difficult to align adequately (and hence requires gears for synchronization). Richards further leaves to the imagination the actual fluid connections required to function. DeLancey U.S. Pat. No. 2,121,120 is a crossed-piston flowmeter, but it is not epicyclic, and uses rollers and cams moved by its pistons, to produce uniform shaft rotation proportional to volumetric displacement in the chambers. There is no rotation of the cylinders. Smith U.S. Pat. No. 2,661,699 is a crossed-piston engine with a conventional crank, stationary cylinders and sliding (“Scotch’) yokes connecting the pistons to the connecting rods, similar to Guinard's device. The Smith engine is not epicyclic. Johnson U.S. Pat. No. 2,684,038 is another crossed piston design with scotch yokes, but with yokes in the connecting rods' centers, rather than at the pistons as in Smith. DeLancey, Smith, and Johnson are all cited by Richards. In addition, none of these patents describe a combination of pressure chambers and vacuum chambers in a single device. Moreover, the existing patents all describe oil-lubricated devices and do not describe a concentrator system in oil-free form.
The more relevant patents citing Richards include Baker U.S. Pat. No. 3,977,303. Baker is epicyclic, but includes a free-rotating secondary eccentric between his crankshaft and pistons, all within a non-rotating cylinder block. Gail U.S. Pat. No. 5,375,564 teaches an oil-lubricated epicyclic engine with three or more piston axes (and cites Avermaete U.S. Pat. No. 3,665,811, another 3-cylinder epicyclic engine; Lamm U.S. Pat. No. 3,799,035 which teaches a spinning epicyclic engine or pump similar to the present invention; and Froumajou U.S. Pat. No. 3,921,602 which describes an engine of complex epicyclic form in which the pistons describe multiple strokes per revolution, where eccentricities of the rotating elements have non-unity integer ratio). Farrington U.S. Pat. No. 6,148,775 discloses an engine with the epicyclic kinematics of the present invention.
What is needed is a compact, balanced, and low-cost oil-free pump that can serve either simple PSA, the more efficient and compact VPSA systems or both PSA and VPSA. Compactness and balance are of special value to portable concentrators, and low cost is of greater value in stationary units.